In clinical diagnostics the examination of body fluids enables an early and reliable detection of pathological states as well as the targeted and well-founded monitoring of physical conditions. Nowadays individual analyses that are specifically directed towards one parameter often require a few microliters of blood and even down to less than one microliter. Blood is typically collected by piercing the skin of the person to be examined, e.g. the finger pad or the earlobe with the aid of a sterile sharp lancet. This method is especially suitable when the analysis of the blood sample can be carried out directly after blood collection.
Substrate-based spot-monitoring tests are well established for the chemical and biochemical analysis of body fluids in specialized laboratories for these analyses but in particular also for use outside permanent laboratories. Such substrate-based spot-monitoring tests based on a specifically developed dry chemistry can be carried out simply and in an uncomplicated manner even by laymen despite the often complex reactions involving sensitive reagents. The most prominent examples of substrate-based spot-monitoring tests are test strips for determining the amount and/or concentration of blood glucose in diabetics.
In the diagnostic tests that are used nowadays for detecting an analyte (e.g. blood glucose) in a body fluid (e.g. blood), the function of lancing to generate a skin opening and the concentration determination function are typically divided among several components, e.g. a lancing device for lancing and generating a drop of blood, and an analytical test element e.g. a test strip for receiving the drop of blood, passing the blood from the receiving site to the reaction area and determining an analyte, e.g. blood glucose.
Lancets and suitable devices for them which enable a relatively painless and reliable collection of blood are offered generally in the field of so-called “home-monitoring”, i.e. where patient consumers themselves carry out simple analyses of blood and in this case especially for the periodic blood collection by diabetics that often has to be carried out several times daily to monitor the blood glucose concentration. Examples of lancets and lancing devices are the commercially available devices and lancets Glucolet® from Bayer AG and Soflclix® from Roche Diagnostics GmbH. Such lancets and devices are for example the subject matter of WO 98/48695, EP 0,565,970, U.S. Pat. No. 4,442,836 or U.S. Pat. No. 5,554,166, each incorporated herein by reference.
The self determination of blood glucose is nowadays a world-wide method in diabetes monitoring. Blood glucose instruments in the state of the art such as the AccuChek® Advantage (from Roche Diagnostics) consist of a measuring instrument into which a test element (test strip) is inserted. The test strip is for example brought into contact with a drop of blood which has been previously collected from the finger pad by means of a lancing device. On the test strip the blood is transported into the area in which the reagent chemistry is located. Here the analyte to be analyzed reacts with the reagent chemistry and generates a measurement signal, e.g. an electrical current impulse or a change in color. The measurement signal is evaluated by the measuring instrument and a timely blood glucose value is shown to the user on the display of the blood glucose instrument.
In order to rigorously monitor the blood glucose content it is necessary to regularly carry out glucose measurements for example several times daily. A new test strip which is provided in storage vials containing for example 50 strips is required for each measurement. In this regard it should be born in mind that the test strips can have a different quality and different properties depending on the strip lot which can influence the measured result. It is therefore often necessary to calibrate the glucose measuring instrument before inserting the measurement strip. These variations are typically due to unavoidable tolerances during test strip manufacture and/or the reagent chemistry. In order to compensate for this, a large number of samples of each production lot are measured and lot-specific calibration data are determined from these measurements. These data are delivered to the customer together with the test strips, but are not necessarily visible to the customer. The set of data consists of a lot number and values which describe a correction function.
In many known measurement systems, it is known to provide a number code on the storage container for the test strips which has to be entered by means of an appropriate input unit on the glucose measuring instrument in order to adjust the glucose measuring instrument to the test strips in this container. It is also known to provide a film foil in each test strip container. In that case, the transparent film foil contains a barcode which contains the coefficients of a polynomial of the nth order in binary code. In other known systems, such as in the case of the glucose measuring instruments Accu-Chek Compact® and Accu-Chek Comfort® from Roche Diagnostics GmbH, an electronic storage medium, a so-called ROM key, on which a complete set of the coefficients of a polynomial is stored (see U.S. Pat. No. 5,053,199), is enclosed with the test strips. This ROM key is inserted into the measuring instrument, the data are read from the storage medium by the measuring instrument and used for the correction calculation. Furthermore, U.S. Pat. No. 6,689,320 also describes an electronic data carrier which, however, is inserted into the measuring instrument in a so-called code carrier; in this case the data are transferred using a transponder.
A common feature of all aforementioned calibration methods is that the user has to carry out a large number of steps in order to calibrate the glucose measuring instrument to the test strip lot. There is a risk that errors may occur in the manual input or that one forgets to insert the ROM key or insert the film foil with the lot-specific code. Especially when the user is using several containers containing test strips, there is a risk that a calibration of the glucose measuring instrument to the current test strip lot may be forgotten. In order to avoid this risk, it is known to provide a lot-specific identification in the form of a bar code or magnetic strip on the test strips themselves in addition to the external data store which contains the calibration data. In any event, special care must be taken that despite the separate test strip and data carrier logistics, it is ensured that the correct correction values are enclosed with the test strips.
One method of avoiding the risk of confusion and error is to directly connect the entire calibration data with the test strip. The test strip for the Reflochek® from Roche Diagnostics GmbH for example has a bar code printed on, and a magnetic strip is glued onto the Reflotron® strip (Roche Diagnostics GmbH).
However, as the development progresses towards smaller and smaller test strips and at the same time more and more calibration data, the data capacity of such miniaturized bar code or magnetic strips reaches its limits.
Hence DE 102 37 602 describes a system for blood glucose measurement in which a data carrier with adequate capacity is present on the test strip itself in order to store all required data on the strip. The calibration unit in this blood glucose measuring system comprises a receiver unit which interacts with a transmitter unit on the test strip for the wireless transmission of a signal which reflects the quality and/or the properties of the test strip. This wireless and non-contacting transmission of calibration data means that the user does not have to carry out any additional steps for calibration of the instrument to the currently-used test strip. It is only necessary that the test strip is held near to the measuring instrument, which is the case, for example, when the strip is inserted into the measuring instrument. The receiver unit and the transmitter unit in this case fort a so-called transponder system.
R. Puers describes a transponder system which is used in orhthopaedic implants (“Linking Sensor Systems with Telemetry: Impact on the System Design”, Sensors and Actuators (1996) 169-174).
J. Black et al. describe an implantable amperometric glucose sensor with an integrated telemetry unit as an example for transmission of analogue data (“Integrated Sensor-Telemetry System for in vio Glucose Monitoring”, Sensor and Actuators (1996) 147-153).
A heart pacemaker is described in WO 031 00942 which receives its energy via a transponder from an extracorporeal battery unit. In return the heart pacemaker transmit its charge state to the outside.
U.S. Pat. No. 6,217,744 concerns a disposable test strip for blood glucose measurement which transmits its measurement data via a transponder to the information device where the blood sample itself serves as an electrolyte for the battery in the disposable.
In view of the foregoing, it is an object of the present invention to employ, in the context of a system for determining the concentration of an analyte in a bodily fluid, a transponder system that comprises a reading/receiving system, which corresponds to the aforementioned receiver unit in the measuring instrument, and the actual transponder, which corresponds to the aforementioned transmitter unit on the test strip. The energy required for the measurement can be provided to the test strip by the receiving system, i.e. the test strip does not have its own power supply. In one useful embodiment, the transmitter unit on the test strip transmits the stored calibration data as well as the measured signals of the current measurement to the measuring instrument.
Transponders are typically provided with microprocessors in silicon technology. Although the manufacturing costs for silicon chips have decreased considerably in recent years due to miniaturization, integration and optimization of the manufacturing processes, they are nevertheless still at such a high level that they would disproportionately raise the cost of a measurement if each individual test strip that is discarded after a single measurement would be equipped with such a silicon chip. To overcome this and satisfy the objects of the present invention, a more practical embodiment of a transponder system is disclosed herein.